1. Field of the Invention
This invention is directed to a pelvic alignment assembly designed to be used during a total hip replacement surgery for purposes of accurately positioning a prosthetic acetabular cup in the hip joint socket by reproducing precise anatomical alignment of the pelvis. More in particular, immediately prior to the insertion of the acetabular cup, a surgeon utilizing the pelvic alignment assembly of the present invention can re-position the patient, typically by forward or backward rotation of the patient, and determine when the pelvis has accurately assumed a pre-determined "baseline" or reference position, initially established at the beginning of the surgical procedure, which is substantially indicative of a true lateral position or a true anterior-posterior position of the pelvis, and thereby, optimize the accurate positioning of the acetabular cup within patient's the hip joint socket.
2. Description of the Related Art
As people age, it is relatively common for there to be some deterioration of the hip joint, and more in particular, of the head of the femur or thigh bone, with the result often being that many such persons will have to undergo a total hip replacement ("THR") surgery performed by an orthopedic surgeon. A total hip replacement surgery involves the use of a prosthetic femoral component comprised of a stem that fits into the upper femur. On the upper or proximal aspect of the stem is a ball which will function to replace the patient's damaged or worn out femoral head. To accommodate placement and positioning of the femoral component within the hip joint, it is necessary to insert a prosthetic acetabular cup to receive the ball-like end of the femoral component in substitution for the socket of the human hip joint. In order to achieve optimum performance of these cooperative prosthetic components, the acetabular cup must be positioned as accurately as possible within the pelvis of the patient. Inaccurate positioning or alignment of the acetabular cup within the hip joint can present extensive and serious problems to the patient after surgery and the requisite healing period, such as providing the patient with a decreased range of motion, the subsequent and possibly accelerated loosening or failure of either or both of the acetabular and femoral components, as well as possible dislocation of the hip joint. Following surgery and progressively over the first year subsequent to surgery, scar tissue normally forms about the inserted prosthetic components, which serves to recreate a hip joint capsule called a pseudocapsule which typically aids in the prevention of hip dislocation. However, when the acetabular cup is oriented in a less than an optimal angular position, hip dislocation is thought to be much more likely even when the patient is performing normal, everyday activities which require the hip joint to pass through a normal range of motion. Hip dislocation is one of the most dreaded complications after THR surgery and it is quite well understood in the medical profession that the most common reason for post-operative total hip dislocation is less than optimally positioned acetabular components, also known as acetabular malposition.
In properly orienting the acetabular cup for receipt of the prosthetic femoral component, it is necessary to accurately establish both the abduction angle as well as the anteversion angle. Typically, the anteversion angle, also known as forward flexion, is generally in the range of about 10 degrees to about 25 degrees. The abduction angle is typically in the range of about 35 degrees to 50 degrees, with a most preferred angle being at or about 45 degrees. Due to the well recognized fact that an improperly positioned acetabular component can subsequently cause the patient numerous problems, as set forth above, a number of devices or instruments have been designed to aid in the proper positioning and/or alignment of the acetabular cup. These known devices have included cup positioners which comprise a pusher ball that is sized and shaped to fit the recess formed within the acetabular component, along with one or more positioned arms, a positioned flange juxtaposed to the pusher ball and a pusher arm connected to the ball and to the flange, to enable the user to push the acetabular cup, when it is resting on the flange into the patient's prepared acetabulum during the THR surgery. However, in the utilization of such devices, the pelvis of the patient should have been properly oriented in either a true anterior-posterior or a true lateral position in order to accomplish an optimal, predicted cup position. There has been, unfortunately, almost a complete lack of devices in the medical field to help with accurately achieving an established pelvic position, and this has left the surgeon to estimating, to the best of his or her ability, the position or alignment of the pelvis in order to utilize the known devices or instruments, discussed above, for positioning of the prosthetic acetabular cup within the hip joint. Estimation of the pelvic position, in the manner set forth above, frequently involves only the surgeon's visual observation of the patient's orientation in an effort to accomplish the desired pelvic alignment. It is further encumbered by so little of the patient's body being exposed during surgery because of the sterile surgical drapes covering the patient. As such, it is not uncommon to misjudge the anatomical alignment of the pelvis, particularly where the patient suffers from obesity, congenital abnormalities, or bone and/or soft tissue destruction from previous surgeries. In addition, there are close tolerances involved in accurately establishing both the anteversion angle and the abduction angle, discussed above. Therefore, the use of known devices of the type set forth above, or the unintentional failure to accurately determine the anatomical alignment of the pelvis in a true anterior-posterior or true lateral position, may very well result in the acetabular component being improperly positioned when implanted into the pelvis of the patient.
As such, there is a long felt need in the art for reliable, medical instrumentation which would be capable of accurately establishing a proper or preferred anatomical position of a patient's pelvis, which may be defined to mean a true anterior-posterior position or a true lateral position of the pelvis during a THR surgery. More in particular, prior to the implantation of the acetabular cup into the patient's pelvis, the pelvis should be repositioned into a predetermined position in order to optimally implant and orient the acetabular component related to the prosthetic femoral component, which as discussed above, can reproducibly only be accomplished if the pelvis of the patient is properly oriented in either a true anterior-posterior or a true lateral position. If an alignment assembly were developed to properly re-orient the patient in such a position, it would greatly enhance the surgeon's ability to optimally and reproducibly position the acetabular cup, and thereby, be more likely to result in the patient's being able to function through a normal range of movement, with a greatly decreased fear of either hip dislocation or accelerated deterioration of the implanted prosthetic components. If any such alignment assembly were developed, it would preferably include a visually observable instrument structured to facilitate the establishment and/or re-establishment of a baseline or reference position of the pelvis, when in its normal or proper anatomical alignment defined by a true anterior-posterior position or true lateral position. More specifically, any such alignment assembly should be structured so as to be capable of being adjustably oriented or positioned to reestablish the aforementioned baseline or reference position, indicative of proper pelvic alignment of the patient, and thereby, to more reliably assure the accurate placement of the acetabular cup.